In current starter systems for automotive vehicle engines, a solenoid and a mechanical linkage are employed to move the starter pinion into engagement with the ring gear and to close switch contacts to energize the starter motor. A spring is used to disengage the pinion and open the switch contacts when the solenoid is deenergized. Spiral flutes on the shaft of the starting motor cause the inertial and load torque to aid the engagement when the motor is energized and to aid disengagement when it is deenergized.
At an earlier time, a somewhat different starter system was commonly used in automobiles. In this system, there was no solenoid and the engagement and disengagement of the pinion and ring gear was effected solely as the result of inertial and load torque cooperating in conjunction with spiral flutes on the starter shaft. The difficulty with this system is that it has a tendency to disengage when the engine overruns the starter motor. By the addition of the solenoid, as in the above-mentioned starter system, the gears are held in engagement for as long as power is applied to the starter motor.
Another arrangement has been proposed to retain the pinion and ring gear in engagement when the engine momentarily overruns the starter motor, without the use of a holding solenoid. In this, a centrifugal detent device retains the starter drive in its advanced or gear engaging position even though there is a momentary overrunning by the engine. Such an arrangement is shown in the Sabatini U.S. Pat. No. 3,090,242 and in the McMillen U.S. Pat. No. 4,308,462.
In order to ensure that the helical cam arrangement provides positive advance of the starter drive, it has been proposed to provide braking means for restraining the starter drive against rotation until the pinion reaches engagement with the ring gear. Reliance upon inertial forces alone to produce the relative angular displacement required has been found to be unsatisfactory. Additionally, braking of the starter drive against rotation also aids in meshing of the pinion with the ring gear without clash. An electromagnetic brake arrangement for the starter drive during its advance toward gear engagement in which the electromagnet travels with the starter drive is shown in the Giometti U.S. Pat. No. 3,572,133. Another electromagnetic brake arrangement in which stationary electromagnets coact with the pinion is described in the Isley et al U.S. Pat. No. 2,926,265.
It is desirable, especially with a starter drive having a centrifugal detent, to provide for braking of the starter motor when it is deenergized to aid in the retraction of the pinion. The is especially important at high motor speed where the latching force of the detent is so great that the forces resulting from deceleration are insufficient to force the detent to release. With braking of the motor, the motor speed is reduced in a fraction of a second to a point where the detent will release. Dynamic braking of a starter motor with a permanent magnet field is disclosed in the McMillen U.S. Pat. No. 4,308,462.
In starter drives of the type having a brake for restraining rotation thereof during advancing movement toward pinion engagement, there is a problem of avoiding or delaying brake engagement during retraction of the pinion which would cause it to be advanced again after the engine is started. Also, it is desirable to provide a biasing force to maintain the starter drive in its retracted position to avoid clash of the pinion with the ring gear due to vibrations and accelerations in the normal operation of the vehicle.
A general object of this invention is to provide an improved starter drive which overcomes certain disadvantages of the prior art.